1. Field of the Invention
This present invention relates to compositions and processes for oil and gas field applications. More specifically, this invention relates to compositions useful for controlling and/or delaying the gelation of an aqueous composition in a subterranean zone.
2. Description of Related Art
It is well known to those skilled in the art that certain polymers and other compounds are useful in oil and gas field operations. Such oil and gas field chemicals include gel-forming or cross-linking agents.
Allison et al., U.S. Pat. No. 4,773,481 describes a process for reducing the permeability of a subterranean formation by the cross-linking of water soluble polymers of polyalkylene imines and polyalkylenepolyamines with certain polymers which are anionic or hydrolyzable to form anionic polymers. Examples of the anionic polymers are polyacrylamide and alkylpolyacrylamides, copolymers of polyacrylamide and alkylpolyacrylamides with ethylene, propylene and styrene, polymaleic anhydride, and polymethylacrylate and hydrolysis products thereof. As described in the patent, when the water-soluble polymer and the anionic polymer are mixed, a viscous gel is quickly formed. Hardy, U.S. Pat. No. 6,196,317 teaches the use of a metal ion (e.g., zirconium) as a chelator to decrease the gel time.
Thus, there are continuing needs for improved methods and compositions for reducing the permeabilities of subterranean zones using water soluble polymeric components whereby the cross-linking of the components is effectively and simply controlled. In the present invention, a polyelectrolyte complex is used as a gelling agent, but the time for gelation is desirably delayed for a period of time. To date, polyelectrolytes have largely been used in the pharmaceutical industry to improve drug delivery. See, e.g., Prokop et al., U.S. Pat. No. 6,726,934 entitled Micro-particulate and nano-particulate polymeric delivery system; Tiyaboonchai et al., Formulation and Characterization of Amphotericin B-polyethylenimine-dextran sulfate nanoparticles, Int'l Journal of Pharmaceutics, 90, 902-914 (2001); Tiyaboonchai et al., Insulin containing polyethylenimine-dextran sulfate nanoparticles, Int'l Journal of Pharmaceutics, 225, 139-151 (2003). The present invention is the directed to the new use of such polyelectrolyte complexes as controlled or delayed gelling agents.